1. Field of the Invention
The present invention relates to an active vibration damping device for use as an automotive engine mount, body mount, or the like in order to produce active or countervailing damping action of vibration to be damped, and relates in particular to an active vibration damping device adapted to provide active vibration damping action by means of employing an oscillation member to constitute part of the wall of a pressure receiving chamber with a non-compressible fluid sealed therein, and controlling pressure within the pressure receiving chamber by means of exciting actuation of the oscillation member with a solenoid type actuator.
2. Description of the Related Art
Active vibration damping devices that reduce vibration actively and/or in compensating manner by means of imparting excitation force to a member to be damped or to a vibration damping device are known as one type of damper or other vibration damping device for installation in a vibration damping support or vibration damping connector interposed between components making up a vibration transmission system, or on members to be damped.
Such a vibration damping device typically comprises a pressure receiving chamber a portion of whose wall is composed of a main rubber elastic body linking a first mounting member and a second mounting member; and an oscillation member making up part of the wall of the pressure receiving chamber, and actuated from the outside under the control of an actuator. Such devices are taught in JP-A-9-49541 and JP-A-2000-283214, for example. In this kind of active vibration damping device, pressure within the pressure receiving chamber is regulated according to the input vibration to be damped, so as to be able to cancel out the input vibration to provide active vibration damping action.
Fluid filled type active vibration damping devices of this kind are often mass produced and shipped as a series. Thus, in terms of achieving better commercial value and reliability in active vibration damping devices as commercial products, it is essential to minimize deviation in vibration damping characteristics among individual units, so that more consistent characteristics are provided over the entire series.
Accordingly, thoroughgoing quality control of the electromagnetic actuator installed in the vibration damping device unit has been contemplated. The electromagnetic actuator typically has a structure wherein a stator having a yoke member attached about a coil to form a stator-side magnetic path is housed within a housing affixed to the vibration damping device unit, and a moving member is positioned displaceably in the axial direction in a center hole in the stator. In an electromagnetic actuator of this kind, it is contemplated to carry out quality control such that to the greatest extent possible a constant value is maintained for the relative positional relationship of the stator to the magnetic gap disposed on the magnetic path formed by the coil. This is because the output level of an electromagnetic actuator is determined depending on the distance separating the stator and the yoke member forming the magnetic gap on the magnetic path.
In active vibration damping devices of this kind to date, it was extremely difficult to minimize deviation in the distance separating the yoke member and the stator, among individual units of product.
The reason is that typically, a rubber elastic body is used for the purpose of displaceably supporting the oscillation member. However, since a rubber elastic body can experience molding shrinkage, it is not possible to control dimensions with high accuracy, unlike metal fittings. Additionally, permanent set in fatigue of the rubber elastic body in association with deterioration over time can be the cause of deviation in the distance separating the yoke member and the stator.
Furthermore, the distance separating the yoke member and the stator can be affected by component dimension errors or assembly errors of the yoke member or stator per se, or of components that directly or indirectly relate to positioning thereof.
In this way, the distance separating the yoke member and the stator is determined by numerous factors, and it is impossible to control all of these numerous factors with a high degree of accuracy. In addition to the fact that settings for the separating distance are extremely small, since magnetic acting force varies exponentially depending on the distance between magnetic poles, such small deviations will be manifested as very large deviations in vibration damping characteristics among individual active vibration damping devices.